By mid-1953 these had developed into a form very similar to the final DC-8; an 80-seat, low-wing aircraft with four [Vous devez être inscrit et connecté pour voir ce lien] turbojet engines, 30° wing sweep, and an internal cabin diameter of exactly 11 ft (3.35 m) to allow five abreast seating.

Maximum weight was to be 95 tons (86 tonnes), and range was estimated to be about 3,000-4,000 mi (4,800-6,400 km).

Douglas remained lukewarm about the jet airliner project, but believed that the Air Force tanker contract would go to two companies for two different aircraft, as several USAF transport contracts in the past had done.

In May 1954, the USAF circulated its requirement for 800 jet tankers to Boeing, Douglas, Convair, Fairchild, Lockheed, and Martin.

Boeing was already just two months away from having their prototype in the air. Just four months after issuing the tanker requirement, the USAF ordered the first 29 [Vous devez être inscrit et connecté pour voir ce lien] from Boeing.

Even leaving aside Boeing's ability to supply a jet tanker promptly, the flying-boom air-to-air refueling system — as first fitted to the KC-97 — was also a Boeing product: developing the KC-135 had been a safe bet.

[Vous devez être inscrit et connecté pour voir ce lien] was shocked by the rapidity of the decision which, he said, had been made before the competing companies even had time to complete their bids. He protested to Washington, but without success.

Having started on the DC-8 project, Douglas decided that it was better to press on than give up.

Consultations with the airlines resulted in a number of changes: the fuselage was widened by 15 in (38 cm) to allow six-abreast seating.

This led to larger wings and tail surfaces and a longer fuselage.

The cost of the program was enormous; it was at that time the most expensive venture of any kind ever taken on by a single company.

Donald Douglas provided $450 million towards it out of his own pocket.

Four versions were offered to begin with, all based on the same 150 ft 6 in (45.9 m) long airframe with a 141 ft 1 in (43 m) wingspan, but varying in engines and fuel capacity, and with maximum weights of about 120-130 tons (109-118 tonnes).

Douglas steadfastly refused to offer different fuselage sizes.

The maiden flight was planned for December 1957, with entry into revenue service in 1959.

Well aware that they were lagging behind Boeing, Douglas began a major push to market the product.

At the time, Douglas' previous thinking about the airliner market seemed to be coming true; the transition to turbine powered looked likely to be one to turboprops rather than turbojets.

The pioneering 40–60-seat [Vous devez être inscrit et connecté pour voir ce lien] was already in service and proving enormously popular with both passengers and airlines: it was much faster, quieter and more comfortable than piston-engined types.

Meanwhile the Comet remained grounded, the French 90-passenger twin jet [Vous devez être inscrit et connecté pour voir ce lien] prototype had just flown for the first time, and the 707 was not expected to be available until late 1958.

The major airlines were reluctant to commit themselves to the huge financial and technical challenge of jet aircraft.

On the other hand, no-one could afford not to buy jets if their competitors did.

Douglas made a massive effort to close the gap with Boeing, using no less than ten individual aircraft for flight testing to achieve [Vous devez être inscrit et connecté pour voir ce lien] certification for the first of the many DC-8 variants in August 1959.

Much had needed to be done: the original air brakes on the lower rear fuselage were found ineffective and were simply deleted as engine thrust reversers had become available; unique leading-edge slots were added to improve low-speed lift; the prototype was 25 kn (46 km/h) short of its promised cruising speed and a new, slightly larger wingtip had to be developed to reduce drag.

The DC-8 entered revenue service first with [Vous devez être inscrit et connecté pour voir ce lien] on 18 September 1959 with United also entering service later on the same day.

[Vous devez être inscrit et connecté pour voir ce lien] By March 1960, Douglas had reached their planned production rate of eight DC-8s a month. Despite the large number of DC-8 early models available, all used the same basic airframe, differing only in engines, weights and details.

In contrast, Boeing's rival 707 range offered several fuselage lengths and two differing wingspans: the original 144 ft (44 m) 707-120, a 135 ft (41 m) version that sacrificed space to gain longer range, and the stretched 707-320, which at 153 ft (46.5 m) overall had 10 ft (3 m) more cabin space than the DC-8.

Douglas' refusal to offer different fuselage sizes made it less adaptable, and the DC-8 gradually lost market share to Boeing.

After an excellent start, 1962 DC-8 sales dropped to just 26, followed by 21 in 1963 and 14 in '64, and most of these were for the Jet Trader rather than the more prestigious passenger versions.